Received-SPF: pass (google.com: domain of linux-kernel+bounces-167993-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:4601:e00::3 as permitted sender) client-ip=2604:1380:4601:e00::3;
Date: Fri, 3 May 2024 10:55:33 -0700
From: Kees Cook <keescook@chromium.org>
To: Thomas =?iso-8859-1?Q?Wei=DFschuh?= <linux@weissschuh.net>
Cc: Alexander Popov <alex.popov@linux.com>, linux-hardening@vger.kernel.org,
	linux-kernel@vger.kernel.org, stable@vger.kernel.org,
	Luis Chamberlain <mcgrof@kernel.org>,
	Joel Granados <j.granados@samsung.com>
Subject: Re: [PATCH] stackleak: don't modify ctl_table argument
Message-ID: <202405031054.9FFA75B@keescook>
References: <20240503-sysctl-const-stackleak-v1-1-603fecb19170@weissschuh.net>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <20240503-sysctl-const-stackleak-v1-1-603fecb19170@weissschuh.net>

On Fri, May 03, 2024 at 03:44:09PM +0200, Thomas Wei?schuh wrote:
> Sysctl handlers are not supposed to modify the ctl_table passed to them.
> Adapt the logic to work with a temporary
> variable, similar to how it is done in other parts of the kernel.
> 
> This is also a prerequisite to enforce the immutability of the argument
> through the callbacks prototy.
> 
> Fixes: 964c9dff0091 ("stackleak: Allow runtime disabling of kernel stack erasing")
> Cc: stable@vger.kernel.org

I realize I've already Acked, but does this actually need to be CCed
to stable?

> Acked-by: Kees Cook <keescook@chromium.org>
> Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
> Signed-off-by: Thomas Wei?schuh <linux@weissschuh.net>
> ---
> This was split out of my sysctl-const-handler series [0].
> 
> As that series will take some more time, submit the patch on its own,
> as it is a generic bugfix that is valuable on its own.
> And I can get it out of my books.
> 
> Changelog in contrast to the patch in the series:
> * Reword commit message to remove strong relation to the constification
> * Cc stable
> 
> [0] https://lore.kernel.org/lkml/20240423-sysctl-const-handler-v3-0-e0beccb836e2@weissschuh.net/
> 
> Cc: Joel Granados <j.granados@samsung.com>
> ---
>  kernel/stackleak.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/stackleak.c b/kernel/stackleak.c
> index 34c9d81eea94..b292e5ca0b7d 100644
> --- a/kernel/stackleak.c
> +++ b/kernel/stackleak.c
> @@ -27,10 +27,11 @@ static int stack_erasing_sysctl(struct ctl_table *table, int write,
>  	int ret = 0;
>  	int state = !static_branch_unlikely(&stack_erasing_bypass);
>  	int prev_state = state;
> +	struct ctl_table tmp = *table;
>  
> -	table->data = &state;
> -	table->maxlen = sizeof(int);
> -	ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
> +	tmp.data = &state;
> +	tmp.maxlen = sizeof(int);
> +	ret = proc_dointvec_minmax(&tmp, write, buffer, lenp, ppos);
>  	state = !!state;
>  	if (ret || !write || state == prev_state)
>  		return ret;

I can pick this up; thanks!

-Kees

> 
> ---
> base-commit: f03359bca01bf4372cf2c118cd9a987a5951b1c8
> change-id: 20240503-sysctl-const-stackleak-af3e67bc65b0
> 
> Best regards,
> -- 
> Thomas Wei?schuh <linux@weissschuh.net>
> 

-- 
Kees Cook